In recent years, the hydrolysis of a polysaccharide (e.g., cellulose or starch that comprises a plant body) to produce a monosaccharide that can be fermented with yeast or the like has been focused as an essential technique for producing a clean fuel “bioethanol”. The hydrolysis of a polysaccharide is also important, not only for the production of a monosaccharide, but also as a method for producing a chemically or nutritionally useful substance. Not only the hydrolysis of a water-insoluble cellulose or the like into a water-soluble substance is important as a means for producing a chemically or nutritionally useful substance, but the hydrolysis also enables to produce a monosaccharide readily through enzymatic saccharification of the water soluble substance which produced by the hydrolysis of the water-insoluble cellulose or the like. The monosaccharide can be used for the production of “bioethanol” through fermentation or the like. Thus, the hydrolysis of a water-insoluble polysaccharide is highly valuable from the industrial viewpoint. In the hydrolysis reaction, up to this time, either of “a concentrated sulfuric acid method” or “a diluted sulfuric acid method” has been employed (Non-patent reference No. 1). In the “concentrated sulfuric acid method”, a polysaccharide is hydrolyzed in concentrated sulfuric acid. However, an enormous amount of energy is required for separating a product of the reaction, such as a monosaccharide or a water-soluble hydrolysate, from sulfuric acid. In the “diluted sulfuric acid method” utilizing diluted sulfuric acid of 100° C. or higher, on the other hand, an enormous amount of energy is required not only for the separation of a product such as a monosaccharide or a water-soluble hydrolysate from sulfuric acid, but also for the reaction itself. When a solid acid which can be separated from a product readily is used as a catalyst, a large amount of energy cost can be saved. However, there is found no solid acid that can hydrolyze a polysaccharide such as cellulose or starch that comprises a plant body and enables to produce a monosaccharide capable of being fermented with yeast or the like or a chemically useful intermediate such as a low-polymeric saccharide efficiently. Study has been made on the method for decomposing cellulose with an enzyme. However, the method has such problems that an expensive enzyme must be used and that the hydrolytic activity of an enzyme used is low (Non-patent reference No. 2).
The present inventors found that a carbonaceous material having sulfonic acid group therein which is characterized by being produced by the carbonization and sulfonation of an organic material can act as a catalyst, and filed patent applications previously (Patent reference Nos. 1 and 2). However, the patent applications do not describe about a fact that the carbonaceous material can hydrolyze a polysaccharide.    [Non-patent reference No. 1] Bionics, 2006, vol. 2, p. 26-33    [Non-patent reference No. 2] Cellul Chem Technol vol. 26, p 3-10    [Patent reference No. 1] Japanese Patent Application Laid-open No. 2004-238311    [Patent reference No. 2] International Publication No. WO 2005/029508 pamphlet